Loop antenna with distributed impedance near the terminating gap

ABSTRACT

A low cost, physically small loop antenna is provided. The loop antenna is characterized by a metal band arranged in a loop having a pair of separated gaps, one of which is a feed gap and the other an impedance terminating gap. A resistance is coupled across the impedance termination gap. The metal bands have slots therein near the terminating gap to provide a distributed reactance near the terminated gap.

mite States Patent 1 Smalser LOOP ANTENNA WITH DISTRIBUTED IMPEDANCENEAR THE TERMINATING GAP Inventor: Paul Joseph Smalser, Deptford NJ.

Assignee: RCA Corporation, New York, NY.

Filed: Sept. 21, 1972 Appl. No.: 290,801

US. Cl. 343/740, 343/744 1:11.01. H0lq 11/12 Field of Search 343/739,740, 741,

References Cited UNITED STATES PATENTS ll/l97l Dol et al 343/744 1451Sept. 25, 1973 Primary ExaminerEli Lieberman A!t0rneyEdward J. Norton eta].

[57] ABSTRACT A low cost, physically small loop antenna is provided. Theloop antenna is characterized by a metal band arranged in a loop havinga pair of separated gaps, one of which is a feed gap and the other animpedance terminating gap. A resistance is coupled across the impedancetermination gap. The metal bands have slots therein near the terminatinggap to provide a distributed reactance near the terminated gap.

5 Claims, 4 Drawing Figures Patented Sept. 25, 1973 2 Sheets-Sheet 1.

TUNER Win Patented Sept. 25, 1 973 2 Sheets-Sheet mi MSEE l I l I I I1-- WITHOUT SLOTS WITH sLors wnnour SLOTS ram: 35 :55

LOOP ANTENNA WITH DISTRIBUTED IMPEDANCE NEAR THE TERMINATING GAPBACKGROUND OF THE INVENTION 1. Field of the Invention This inventionrelates to a low cost, physically small loop antenna and moreparticularly to an improved very high frequency antenna designed foroperating over the entire range of the VHF television channels. 2.Description of Prior Art A real and substantial need has existed for atruly low cost structurally very small antenna for efficient receptionover the entire very high frequency (VHF) television frequency bands of54 to 88 MHz and 174 to 216 MHz. Further, there is a need in order todiscriminate against multipath signals for the antenna to have a minimumlevel back lobe and to have a means in which obstructions that causeghosts in the television picture be nullified.

The loop antenna is described by Harold H. Beverage in U.S. Pat. No.2,247,743. While this antenna structure provides a cardioid shape in theplane of the loop for some of the VHF television frequencies whenproperly designed using a single resistor, this cardioid shapes variesgreatly over the entire VHF television frequency bands. At some desiredVHF television fre quencies the back lobe becomes significantly largeand permits ghosting. It is also desirable in order to minimize theabove described ghosts that the antenna pattern have deep nulls in theradiation pattern in the rear of the antenna so that an obstructionlocated in the rear of the antenna be located when the antenna isproperly oriented at one of these nulls to nullify the effect of theobstruction and eliminate ghosts in the television picture. It istherefore desirable that these nulls be both significant in the rear andthat they be substantially at the same azimuth angle regardless of theoperating frequency of the antenna.

SUMMARY OF THE INVENTION A loop antenna for operation over the entirevery high frequency television frequency bands is provided by a pair ofmetal bands arranged in a loop. The loop has a pair of gaps with thefirst gap forming a pair of feed terminals and the second gap beingdirectly opposite the first gap and having thereacross a resistance. Themetal bands have slots near the termination gap to provide a distributedreactance termination in series with the resistance. The dimension ofthe loop between the points on the loop midway between the pair of gapsis less than a half length of an operating very high frequency wave. Thevalue of the resistance and distributed reactance being selected so thatthe loop has a maximum response to signals in the very high frequencyband in the direction of the first feed terminal Description of theDrawings A more detailed description follows in conjunction with thefollowing drawing in which:

FIG. 1 is a perspective view of the all channel antenna system accordingto the present invention.

FIG. 2 is a side elevation of one of the metal bands in extended form.

FIG. 3 illustrates typical horizontal radiation patterns at an operatingfrequency of 185 MHz for the VHF loop element with and without thetermination slots.

FIG. 4 illustrates typical horizontal radiation patterns at an operatingfrequency of 63.8 MHz for the VHF loop antenna element with and withoutthe impedance termination slots.

DETAILED DESCRIPTION Referring to FIG. 1, there is illustrated a loopantenna element 10. The loop antenna element 10 includes a pair ofsemicircular metal bands 11 and 13. It is understood that the loopinstead of being circular may be other contours such as square orrectangular. The loop antenna element 10 has an input feed gap acrossterminals 15 and 17. The gap for the above example can be one-half inch.The terminals 15 and 17 are coupled to a pair of conductors l9 and 21which may be coupled to a television tuner. Remote from the input feedgap of the antenna element is a terminating gap between metal bands 11and 13 having terminals 23 and 25. Connected directly across the gapterminals 23 and 25 is a resistor 27. The diameter of the loop antennaelement 10 at points midway between the gaps is made less than half ofthe length of the operating wave )t/2). As an example, for operatingover the VHF television frequency bands (54 MHz to 88 MHz and 174 MHz to216 MHz) the diameter can be about 18 inches with the bands 11 and 13each being about 27.5 inches long. The metal bands 11 and 13 in apreferred arrangement are 2 inches wide across width, w in FIG. 1 with along taper near the feed terminal terminating ends 15 and 17. This taperbegins in the above example about 4 inches from each of the ends 15 and17. This tapering of the ends is to reduce the capacity near the feedterminals.

Referring to FIG. 2, the metal band 11 is shown in extended form. Theend 17 is the feed terminal end and the end 25 is the terminatingimpedance end. The overall length for operating at the VHF televisionbroadcast frequency (54-88 MHz and 174-216 MHz) is on the order of 27.5inches long and the width as mentioned above is 2 inches with a taper atend 17 as described above and a sharper taper at end 25. The taper atend 25 begins about 1 inch from the end 25 and tapers from 2 inches toabout one-half inch at the end 25. Near the end 25 is a pair of slots 41and 42 which extend from the edge 26 parallel to each other along asubstantial portion (length l) of the length of the metal band 11. Forthe above example antenna these slots were made 9.5 inches long. Thewidth of the slots 41 and 42 are made 0.125 inch wide and at the centerstrip 49 between the slots is about one-half inch. The slots 41 and 42act to form distributed reactance sections each about 9.5 inches long infree space and each having a characteristic impedance in the order ofohms.

Referring to FIG. 1, a similar pair of slots 45 and 47 extend from edge24 of metal band 13. The band 13 is identical to band 11 with the slots45 and 47 being 9.5 inches long. The width of each of the slots 45 and47 is 0.125 inch wide and the center strip 51 between the slots 45 and47 is about one-half inch. The total impedance at the termination of theloop 10 appears as two distributed reactance sections in series with theresistor 27. The termination symmetry is provided by having the twodistributed reactance sections on either end of the resistor 27.

Inboard the loop antenna 10 may be placed a UHF antenna system 30 asshown in phantom in FIG. 1. A more detailed description of this antennais described in US. application Ser. No. 212,431 filed Dec. 27, 1971, byDonald W. Peterson and John James Gibson, now US. Pat. No. 3,721,990.

Additional improvement in the directivity for a UHF antenna system 30when placed inside the loop antenna is provided by the L-shaped slots53, 55 in band 11 and the L-shaped slots 57, S9 in band 13. The slots 53and 55 intersect opposite edges 61 and 63 of band 11 about six inchesfrom terminal 17. The slots 53 and 55 extend toward each other for abouta one-half inch and then they extend parallel each other for about 2 if;inches. The slots 53 and 55 are it inch wide. Similarly slots 57 and 59in band 13 intersect edges 65 and 67 of band 13 about 6 inches fromterminal 15. The slots 53 and 55 extend toward each other for aboutone-half inch and then they parallel each other for about 2 inches. Theslots 57 and 59 are A inch wide. Since the distance between the pair ofslots 53 and 55 and the pair of slots 57 and 59 for the above describedarrangement is 6 inches plus 6 inches, plus the one-half inch gapbetween terminals 15 and 17, the overall length is over 12 inches or atleast a half wave length at a frequency within the UHF televisionfrequency band.

Referring to FIG. 3, there is shown a horizontal radiation pattern forthe above described antenna with and without the terminating slots at afrequency of 185 MHz. Note the sizable back lobe associated with theantenna operating at this frequency without the terminating slots. Alsonote the lack ofa deep null in the rear portion of the antenna patternwithout the terminating slots. Note in FIG. 3 the low level back lobeand the deep nulls in the rear radiation pattern with the terminatingslots. if an obstruction such as a building that causes ghosts in thetelevision picture is located in the rear portion of the antenna, theantenna can be oriented slightly so that one of the null areas islocated toward the building and since the radiation pattern in theforward direction is relatively broad the input signal -will remainfairly strong and yet the ghosts caused by the building can beeliminated in the null. Similar patterns are associated with the abovedescribed antenna with the terminating slots at the other televisionhigh VHF band frequencies.

FIG. 4 illustrates a horizontal radiation pattern for the abovedescribed antenna with and without the terminating slots at a frequencyof 63.8 MHz. Note again the reduction of the back lobe with theterminating slots and the deeper nulls in the rear pattern. Similarpatterns are associated with above antenna with the terminating slots atthe other television low VHF band frequencies. A comparison of FIGS. 3and 4 reveals the similar pattern characteristics when operating withthe same antenna with slots at frequencies within the high VHF frequencyband or the low VHF frequency band. Since both the back lobe is reducedand the deep nulls are located at about the same azimuth angleregardless of the television VHF operating frequency with the aboveantenna with the terminating slots, the above antenna with the slotswhen properly oriented so as to nullify any particular obstructions inthe rear should operate satisfactorily over the entire television VHFrange of frequencies.

What is claimed is:

l. A loop antenna for operation over the entire very high frequencytelevision frequency bands comprising:

a pair of metal bands arranged in a loop having a pair of gaps betweensaid metal bands,

a first of said gaps forming a pair of feed terminals and a second ofsaid gaps being directly opposite the first gap,

said loop being dimensioned to provide a linear distance less then ahalf wavelength at the highest frequency within said bands betweenpoints on said loop situated midway between the pair of gaps,

a resistance coupled across said second gap,

said resistance having a predetermined value providing a substantiallymaximum response to signals in the direction of said first gap in saidbands, and

said metal bands having slots near the second gap which are dimensionedto provide a pair of distributed reactances of given values in serieswith said resistance,

said given values of said reactances and said predetermined valueresistance cooperating to achieve low back lobes and said substantiallydeep and uniform nulls in the direction of the second gap over theentire very high frequency television frequency bands with respect tothat obtainable without said slots.

2. The combination as claimed in claim 1 wherein said slots extend alongsaid metal bands from the second gap toward the feed terminal gap.

3. The combination as claimed in claim 1 wherein each of said metalbands has identical slots symmetrically disposed relative to each otheron each side of the second gap.

4. The combination as claimed in claim 1 wherein each of said bands hasa pair of slots extending from said second gap along said metal bandtoward the feed terminal gap.

5. The combination as claimed in claim 4 wherein the length of saidslots is about 9.5 inches and the width of said slots is about 0.125inch.

1. A loop antenna for operation over the entire very high frequencytelevision frequency bands comprising: a pair of metal bands arranged ina loop having a pair of gaps between said metal bands, a first of saidgaps forming a pair of feed terminals and a second of said gaps beingdirectly opposite the first gap, said loop being dimensioned to providea linear distance less then a half wavelength at the highest frequencywithin said bands between points on said loop situated midway betweenthe pair of gaps, a resistance coupled across said second gap, saidresistance having a predetermined value providing a substantiallymaximum response to signals in the direction of said first gap in saidbands, and said metal bands having slots near the second gap which aredimensioned to provide a pair of distributed reactances of given valuesin series with said resistance, said given values of said reactances andsaid predetermined value resistanCe cooperating to achieve low backlobes and said substantially deep and uniform nulls in the direction ofthe second gap over the entire very high frequency television frequencybands with respect to that obtainable without said slots.
 2. Thecombination as claimed in claim 1 wherein said slots extend along saidmetal bands from the second gap toward the feed terminal gap.
 3. Thecombination as claimed in claim 1 wherein each of said metal bands hasidentical slots symmetrically disposed relative to each other on eachside of the second gap.
 4. The combination as claimed in claim 1 whereineach of said bands has a pair of slots extending from said second gapalong said metal band toward the feed terminal gap.
 5. The combinationas claimed in claim 4 wherein the length of said slots is about 9.5inches and the width of said slots is about 0.125 inch.